US4115790A - Device for preventing leakage current in light responsive circuit - Google Patents

Device for preventing leakage current in light responsive circuit Download PDF

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Publication number
US4115790A
US4115790A US05/801,583 US80158377A US4115790A US 4115790 A US4115790 A US 4115790A US 80158377 A US80158377 A US 80158377A US 4115790 A US4115790 A US 4115790A
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US
United States
Prior art keywords
circuit
light responsive
responsive circuit
printed
shield
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US05/801,583
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English (en)
Inventor
Katsuhiko Tsunefuji
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Olympus Corp
Original Assignee
Olympus Optical Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Olympus Optical Co Ltd filed Critical Olympus Optical Co Ltd
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Publication of US4115790A publication Critical patent/US4115790A/en
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
    • G03B7/00—Control of exposure by setting shutters, diaphragms or filters, separately or conjointly
    • G03B7/08—Control effected solely on the basis of the response, to the intensity of the light received by the camera, of a built-in light-sensitive device
    • G03B7/081—Analogue circuits
    • G03B7/083—Analogue circuits for control of exposure time

Definitions

  • the invention relates to a device for preventing a leakage current in a light responsive circuit, and more particularly, to a device which prevents disturbances to a weak signal current of the circuit which may be caused by its leakage to other circuits of different potentials or by a leakage current from the latter circuits.
  • a camera which utilizes an electrical shutter is usually provided with a printed circuit board, which forms the electrical circuit thereof.
  • the printed circuit board is formed by a substrate of an electrically insulating material such as ceramic on which the circuit is printed in a pattern.
  • Discrete components such as transistors, capacitors, resistors, IC elements are mounted on the substrate, while photoelectric transducer element and electromagnet which are used for photometry and for constraining the second screen of the shutter, respectively, are connected with the circuit through lead wires. It will be thus seen that conductors of varying potentials exist on the printed circuit board.
  • FIG. 1 shows a conventional arrangement.
  • a single lens reflex camera 1 of TTL photometry type includes a movable mirror 2, below which is disposed a photoelectric transducer 3 for photometry.
  • a taking lens 4 As is recognized, light passing through a taking lens 4 is led to a film 5, and to a viewfinder system by the mirror 2.
  • a focussing lens 6 is located at a conjugate position to the film 5.
  • the optical system of the viewfinder additionally comprises a condenser lens 7, a pentaprism 8 and a eyepiece 9.
  • Screens of a focal plane shutter are disposed immediately in front of the film 5.
  • a first screen of the shutter is shown at 10, and its surface facing toward the lens 4 is formed to present an optical reflectivity which is equivalent to that of the film surface so that during a photographing operation when the movable mirror 2 is raised to its upper position, the transducer 3 receives reflected light from the first screen 10 during the initial phase and thereafter receives reflected light from the film surface as the screen 10 runs to produce an exposure path in order to allow the shutter circuit to determine a proper exposure period automatically.
  • FIG. 2 shows the electrical shutter circuit including the transducer 3, which is conventional in itself.
  • a substrate 11 of the printed circuit board is shown in phantom lines, and an electrical circuit is printed in a pattern thereon as shown.
  • a number of discrete electrical components which cooperate with the circuit pattern to form the shutter circuit are mounted on the substrate 11, and include an operational amplifier 12 formed as an integrated circuit element, another integrated circuit element 17 which contains an integrator 13, comparison circuit 14, correction circuit 15 and limiter 16, a switching transistor 18, FET 19 which forms a constant voltage source, resistors 20, 21, 22, a trigger switch 23, and a capacitor 24.
  • the substrate is also provided with a pair of terminal pins 25a, 25b across which is connected an electromagnet 26 for constraining the second screen of the shutter, in shunt with a capacitor 27 which bypasses any reverse e.m.f.
  • the substrate is also provided with another terminal pin 28, and a series combination of a main switch 29 and a three volt battery 30 is connected across the terminal pins 28, 25b.
  • a resistor, not shown, is connected across a further pair of terminal pins 31a, 31b for presetting a film speed.
  • the transducer 3 is connected across the input terminals of the operational amplifier 12, which is in turn connected with the integrator 13.
  • the amplifier 12 provides a zero bias across the transducer, and forms a time constant circuit in combination with the transducer and the capacitor 24.
  • the time constant circuit becomes effective to determine the exposure period.
  • a voltage of one volt is applied to the positive input of the amplifier 12 from a contant voltage source comprising FET 19 and resistors 20, 21. Since the amplifier 12 functions together with the integrator 13 to provide a zero bias to the transducer, those conductors on the circuit board which are shown in thick lines in FIG. 2 are of the same potential as the positive input terminal of the amplifier 12, or one volt. It will be noted that these conductors represent an electrical path for a weak signal current from the transducer.
  • FIG. 1 is a schematic view of a single lens reflex camera employing an electrical shutter of TTL photometry type
  • FIG. 2 is a circuit diagram of an exemplary shutter circuit
  • FIG. 3 is a plan view of a device for preventing a leakage current in a light responsive circuit constructed in accordance with one embodiment of the invention.
  • the device of the invention comprises a shield line formed by a printed pattern 34 which surrounds a printed pattern 32 constituting a light responsive circuit and to which the photoelectric transducer 3, capacitor 24 and trigger switch 23 are connected.
  • the patterns 32, 34 are printed on the substrate 11 shown in FIG. 2.
  • the pattern 32 is shown in FIG. 2 by phantom line 33.
  • a voltage of one volt which is equal to the potential of the light responsive circuit is applied to the printed pattern 34.
  • the transducer 3, amplifier 12, trigger switch 23 and capacitor 24 which are electrically connected with the printed pattern 32 are mounted off the surface of the circuit board, so that the pattern 32 is completely isolated by the pattern 34 from other patterns on the circuit board including the 3V conductors.
  • the pattern 32 assumes the same potential as the positive input terminal of the amplifier 12.
  • the shield line or the printed pattern 34 is connected with the positive input terminal of the amplifier 12, the patterns 32 and 34 assume the same potential, thus eliminating any current leakage to or out of the pattern 32.
  • adverse influence of leakage current upon the weak signal current is avoided, enabling a correct photometric current to be obtained. It is to be noted that any leakage current which may flow between the printed pattern 34 and the remainder of the shutter circuit having different potentials cannot affect the operation of the light responsive circuit.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Exposure Control For Cameras (AREA)
  • Camera Bodies And Camera Details Or Accessories (AREA)
  • Shutters For Cameras (AREA)
US05/801,583 1976-06-07 1977-05-31 Device for preventing leakage current in light responsive circuit Expired - Lifetime US4115790A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP51/73844[U] 1976-06-07
JP1976073844U JPS52164527U (ja) 1976-06-07 1976-06-07

Publications (1)

Publication Number Publication Date
US4115790A true US4115790A (en) 1978-09-19

Family

ID=13529846

Family Applications (1)

Application Number Title Priority Date Filing Date
US05/801,583 Expired - Lifetime US4115790A (en) 1976-06-07 1977-05-31 Device for preventing leakage current in light responsive circuit

Country Status (3)

Country Link
US (1) US4115790A (ja)
JP (1) JPS52164527U (ja)
DE (2) DE2723926B2 (ja)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4288694A (en) * 1977-11-02 1981-09-08 Motorola, Inc. High-impedance IGFET input circuit suitable for smoke detector I.C.
US5181065A (en) * 1990-09-04 1993-01-19 Nikon Corporation Flexible printed board for use in cameras

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5717928A (en) * 1980-07-07 1982-01-29 Olympus Optical Co Ltd Photometer against reflection of camera

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3419433A (en) * 1966-05-13 1968-12-31 Nasa Usa Solar cell and circuit array and process for nullifying magnetic fields
US3994001A (en) * 1974-07-02 1976-11-23 Olympus Optical Co., Ltd. Photometric apparatus for single lens reflex camera

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3419433A (en) * 1966-05-13 1968-12-31 Nasa Usa Solar cell and circuit array and process for nullifying magnetic fields
US3994001A (en) * 1974-07-02 1976-11-23 Olympus Optical Co., Ltd. Photometric apparatus for single lens reflex camera

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4288694A (en) * 1977-11-02 1981-09-08 Motorola, Inc. High-impedance IGFET input circuit suitable for smoke detector I.C.
US5181065A (en) * 1990-09-04 1993-01-19 Nikon Corporation Flexible printed board for use in cameras

Also Published As

Publication number Publication date
DE2723926A1 (de) 1977-12-08
JPS52164527U (ja) 1977-12-13
DE2723926B2 (de) 1978-03-23
DE7716752U1 (de) 1982-09-30

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